A bottle generally consists of a shoulder portion with an opening, a side wall or main body which is generally cylindrical in shape, and a bottom joining the side wall. Because of the tendency of the wall of a pressurized plastic bottle to creep under internal pressure, it is a general practice to orient the plastic material and to design the bottle shape in such a way to improve resistance against creep. For the bottom section, it is known that if a uniform material distribution is achieved, the stress caused by the internal pressure can be minimized by using an outwardly hemispherical configuration. Molecular orientation can be obtained by blowing a properly designed parison in a blow mold in the orientation temperature region to enhance the strength of the bottle. The provision of a hemispherical configuration on the base wall of the pressurized plastic container provides for optimum resistance to internal pressure and optimum orientation during the blow molding process. This hemispherical configuration, requires a separate means of support to make the bottle stand upright. For this purpose, a base cup is normally used.
In one commonly used base cup, the base includes a toroidal standing ring for engaging the supporting surface, an annular support ring for engaging the hemispherical wall of the container and an annular curved wall connecting the toroidal standing ring and the support ring. The cup further includes a central disc that is connected by a cylindrical portion and an annular peripheral wall that extends upwardly along a portion of the bottom of the container.
It has been suggested that resistance to axial loads be controlled by preferential permanent deformation of certain portions of the base cup as shown in U.S. Pat. No. 3,927,782 but this obviously affects the appearance of the package.
Such a base cup has proved satisfactory but utilizes a large amount of material. The curved nature of the toroidal standing ring results in lesser stability and high stress concentration. Top load on the package transmitted downwardly is concentrated at the inner portion of the toroidal standing ring resulting in high stress concentration and large deformation. Furthermore, the use of a toroidal supporting ring results in the ring having a smaller diameter than the diameter of the bottle so that the bottle is less stable.
Furthermore, the diameter of the supporting ring is small as compared to the diameter of the bottle resulting in high stress in the bottom wall above the supporting ring.
Accordingly, among the objectives of the present invention are to provide a pressurized fluid package which utilizes a base design that obviates the aforementioned disadvantages and results in increased container stability, lesser stress concentration, increased resistance to top load, less tendency for the container to contact the supporting surface and utilizes a lesser amount of plastic material.
In accordance with the invention a pressurized fluid package comprises an oriented plastic bottle having a generally cylindrical side wall, a neck terminating in a finish or a closure at the upper end, and a hemispherical bottom wall. The base is made of plastic material and comprises a standing ring for engaging a support surface and having a generally planar contacting surface. The base includes a support ring spaced above said standing ring and having an annular surface engaging the hemispherical bottom wall. The base has an annular supporting member extending from the inner periphery of the standing ring and inclined upwardly and inwardly to the outer periphery of the supporting ring, the supporting member being more vertical than horizontal.